New Fluent expander style (#5573)

* Updated Fluent theme Expander style. closes #5358

* Fixed padding mismatch between header and content

* Fixed CornerRadii, unleashed the c o l o u r e s

* Use CornerRadiusFilterConverter instead of expander specific converters

* Formatting

* Fix default theme in ControlCatalog

Co-authored-by: Jumar Macato <16554748+jmacato@users.noreply.github.com>
Co-authored-by: Max Katz <maxkatz6@outlook.com>
# Conflicts:
#	src/Avalonia.Themes.Fluent/Controls/Expander.xaml

samples/ControlCatalog/App.xaml.cs

@@ -39,6 +39,10 @@ namespace ControlCatalog
 
         public static Styles DefaultLight = new Styles
         {
+            new StyleInclude(new Uri("resm:Styles?assembly=ControlCatalog"))
+            {
+                Source = new Uri("avares://Avalonia.Themes.Fluent/Accents/AccentColors.xaml")
+            },
             new StyleInclude(new Uri("resm:Styles?assembly=ControlCatalog"))
             {
                 Source = new Uri("avares://Avalonia.Themes.Fluent/Accents/Base.xaml")
@@ -60,6 +64,10 @@ namespace ControlCatalog
 
         public static Styles DefaultDark = new Styles
         {
+            new StyleInclude(new Uri("resm:Styles?assembly=ControlCatalog"))
+            {
+                Source = new Uri("avares://Avalonia.Themes.Fluent/Accents/AccentColors.xaml")
+            },
             new StyleInclude(new Uri("resm:Styles?assembly=ControlCatalog"))
             {
                 Source = new Uri("avares://Avalonia.Themes.Fluent/Accents/Base.xaml")

src/Avalonia.Themes.Fluent/Accents/Base.xaml

@@ -1,6 +1,7 @@
 <Style xmlns="https://github.com/avaloniaui"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-       xmlns:sys="clr-namespace:System;assembly=netstandard">
+       xmlns:sys="using:System"
+       xmlns:converters="using:Avalonia.Controls.Converters">
   <Style.Resources>
     <!-- https://docs.microsoft.com/en-us/previous-versions/windows/apps/dn518235(v=win.10)?redirectedfrom=MSDN -->
     <!-- SystemColor Color Resources (Reflect OS High Contrast Settings) -->
@@ -30,5 +31,10 @@
     <!-- ScrollBar animation -->
     <TransformOperations x:Key="VerticalSmallScrollThumbScaleTransform">scaleX(0.125) translateX(-2px)</TransformOperations>
     <TransformOperations x:Key="HorizontalSmallScrollThumbScaleTransform">scaleY(0.125) translateY(-2px)</TransformOperations>
+
+    <converters:CornerRadiusFilterConverter x:Key="TopCornerRadiusFilterConverter" Filter="TopLeft, TopRight"/>
+    <converters:CornerRadiusFilterConverter x:Key="RightCornerRadiusFilterConverter" Filter="TopRight, BottomRight"/>
+    <converters:CornerRadiusFilterConverter x:Key="BottomCornerRadiusFilterConverter" Filter="BottomLeft, BottomRight"/>
+    <converters:CornerRadiusFilterConverter x:Key="LeftCornerRadiusFilterConverter" Filter="TopLeft, BottomLeft"/>
   </Style.Resources>
 </Style>